1. Field of the Invention
The present invention relates to a photosensitive member and an image forming apparatus, and more specifically a photosensitive member usable for electrophotography which is configured by consecutively laminating a photoconductive layer containing amorphous Si and a surface protective layer, and an image forming apparatus comprising the photosensitive member according to the present invention.
2. Related Background Art
An electrophotographic apparatus comprising an image forming apparatus such as a copier, a facsimile or a printer forms a copied image or the like by uniformly charging an outer circumferential surface of a photosensitive member having a substrate on a surface of which a photoconductive layer is disposed by charging means for roller charging, fur brush charging or magnetic brush charging, and then exposing an image to be copied of an object to be copied to reflected rays, a laser corresponding to a modulated signal or an LED to form an electrostatic latent image on the outer circumference of the above described photosensitive member, further adhering a toner to the above described photosensitive member to form a toner image and transferring the toner image to copying paper or the like.
After the image is formed by the electrophotographic apparatus as described above, the toner partially remains on the photosensitive member and it is necessary to remove the residual toner. It is general to remove such residual toner at a cleaning step using a cleaning blade, a fur brush, a magnet brush or the like.
By the way, there has recently been proposed and disclosed electrophotographic apparatuses which use no cleaning device so as to produce waste toner in a smaller amount of toner or no waste toner for solicitudes of environments. This type electrophotographic apparatuses are classified into those such as an apparatus disclosed by Japanese Patent Application Laid-Open No. 6-118741 which uses a direct charger such as a brush charger serving for both charging step and a cleaning step, those such as an apparatus disclosed by Japanese Patent Application Laid-Open No. 10-307455 which uses a developing apparatus serving for both a developing step and a cleaning step and others: any apparatus using a step of removing unwanted toner from a surface of a photosensitive member by rubbing the toner with the surface of the photosensitive member.
In recent years where toners which have average particle diameters smaller than conventional are used for enhancing qualities of printed images and toners which have fusion points lower than conventional are used for energy saving, however, it is difficult to remove the residual toner at a toner removing step which is proceeded simultaneously with another process, whereby a problem of toner adhesion may be posed that the above described residual toner interlocks with a surface of a photosensitive member as a result of repeated image formation, thereby producing an image defect of black spots or white spots.
As a measure to solve the above described problem, there has been proposed a method which uses a photosensitive member having amorphous Si as a photosensitive layer and preliminarily roughens, by cutting or with a rotary ball mill, a surface of an electrically conductive substrate on which the above described photosensitive layer is to be formed as disclosed by Japanese Patent Application Laid-Open No. 9-297420, and surface roughness of the substrate as measured with a surface roughness meter is specified on the order of micrometers.
In Japanese Patent Application Laid-Open No. 8-129266, a worked form of an electrically conductive substrate is specified as a value of an average inclination angle xcex8a measured with a surface roughness meter in an evaluation length on the order of millimeters. Furthermore, the value corresponds to 0.0035 to 0.0524 in terms of an average inclination xcex94a.
Furthermore, progresses which have been made in digital electrophotographic apparatuses is forming a main stream of latent image formation with a light source emitting rays having a wavelength such as a laser, an LED or the like. As a result, the above described method which preliminarily cuts the substrate may pose a problem that exposing rays incident on the electrically conductive layer are different dependently on the form of the substrate, thereby forming stripe patterns (interference fringe) on a printed image. Furthermore, a cost is enhanced by newly adding a step of preliminarily roughening the surface of the electrically conductive substrate. When the substrate is worked to roughness within a range where the above described stripe patterns are not produced, in contrast, it may not possible to sufficiently the toner adhesion.
An object of the present invention is to provide a photosensitive member and an image forming apparatus having the photosensitive member which are free from image degradation due to useless toner adhesion to a photosensitive member or a problem due to improper cleaning and capable of maintaining performance for image sharpness not only of an analog image but also of a digital image for a long time.
Furthermore, an object of the present invention is to provide a photosensitive member and an image forming apparatus which prevent a toner from adhering at a cleaning step, thereby providing a favorable image.
Another object of the present invention is to provide a photosensitive member which is composed by laminating a photosensitive layer containing at least amorphous Si and a surface protective layer consecutively on an electrically conductive substrate and has an average inclination xcex94a of 0.12 to 1.0 within a range of 10 xcexcmxc3x9710 xcexcm as well as an image forming apparatus which has the photosensitive member.
The present invention which accomplishes the above described objects is achieved on the basis of a finding that a toner adhesion preventing effect is not always determined by surface roughness of an electrically conductive substrate on the order of micrometers dependent on a worked form of the substrate as measured with a surface roughness meter, but largely dependent rather on microscopic surface roughness (specifically on the order of several nanometers to tens of nanometers) of amorphous Si film (film having a non-single crystal (preferably amorphous) material containing silicon as a parent body). Furthermore, the present invention is based on a finding of a significant correlation between an average inclination xcex94a calculated from this surface shape and the toner adhesion preventing effect.
The average inclination xcex94a within the range of 10 xcexcmxc3x9710 xcexcm indicates a result which is measured with an atomic force microscope (Q-SCOPE 250 (version 3.181) manufactured by Quesant Co.) and it is preferable to measure microscopic surface roughness within a measuring range of 10 xcexcmxc3x9710 xcexcm for obtaining a result with a high accuracy and a high repeatability. Furthermore, it is preferable to carry out correction (tilt removal) of a result obtained with Q-SCOPE 250 manufactured by Quesant Co. to prevent an error from being involved due to curvature and an inclination of a sample. Specifically, a correction (parabolic) for flattening curvature of an AFM image is carried out by fitting the image to a parabolic curve and a correction (line by line) for flattening an inclination is carried out. This technique is preferable for the photosensitive member which is cylindrical. It is possible to appropriately correct an inclination of a sample within a range where data is not distorted as described above.
By controlling the average inclination xcex94a of the amorphous Si photosensitive member measured as described above, it is possible to provide an electrophotographic photosensitive member which is capable of effectively preventing toner adhesion and forming an image which has extremely high quality.
In addition, it is more preferable that the above described average inclination xcex94a has a value within a range of 0.15 to 0.8.
Furthermore, it is possible to prevent the toner adhesion effectively by using a photoconductive layer which is composed of a plurality of layers in addition to a substrate having the above surface roughness.
A variation of a substantial absorption depth for image exposure which is caused by a band gap of the photoconductive layer may produce potential ununiformity of an electrostatic latent image, specifically a residual potential and a ghost potential, whereby fog is produced as a core of the toner adhesion or image sharpness is aggravated.
Furthermore, it is possible to prevent the toner adhesion more effectively by continuously changing a composition in an interface region between the surface protective layer and the photosensitive layer of the photosensitive member.
Specifically, it is desirable to satisfy the following equation (1):
0xe2x89xa6(Maxxe2x88x92Min)/(Max+Min)xe2x89xa60.4xe2x80x83xe2x80x83(1)
where Max (%) denotes a maximum value and Min (%) denote a minimum vale of spectral reflectance in the above described interface region measured within a wavelength range from 450 nm to 650 nm.
The spectral reflectance means here reflectance (percentage) which is measured with a spectrophotometer (MCPD-2000 manufactured by Otsuka Electronic Co.). Outlining determination of the reflectance, a spectral emission intensity I(O) of a light source of a spectroscope is measured, spectral reflected ray intensity of a photosensitive member I(D) is measured and reflectance R=I(D)/I(O) is calculated. For measuring reflectance with a high accuracy and a high repeatability, it is desirable to fix a detector jig so that the detector jig is set at a definite angle relative to the photosensitive member which has curvature.
A specific example of interface control is shown in FIGS. 1A and 1B. An example A (a value of the above described equation (1): 0.48) and an example B (a value of the above described equation (1): 0.41) shown in FIG. 1A are measuring examples xe2x80x9chaving interfacexe2x80x9d, whereas an example C (a value of the above described equation (1): 0.28) and an example D (a value of the above described equation (1): 0.16) are measuring examples xe2x80x9chaving no interfacexe2x80x9d which satisfies the equation according to the present invention. Two lines indicate a difference produced due to a difference between film thicknesses of surface protective layers, and waveform moves dependently on differences between the film thicknesses rightward and leftward on graphs. Since a maximum value of reflectance corresponds to an amplitude of a waveform, reflectance of the photosensitive member having an interface varies more remarkably dependently on a variation of a film thickness than the photosensitive member having no interface at a fixed wavelength. That is, sensitivity varies remarkably dependently on the variation of a film thickness.
That is, fine roughness produces substantial film thickness ununiformity of a surface protective layer in an optical path of incidence for image exposure. It is considered that this film thickness ununiformity causes a sensitivity variation of the photosensitive member having interface which is larger than that of the photosensitive member having no interface, thereby aggravating fog which forms a core of the toner adhesion or sharpness of the image.
Now description will be made of the average inclination xcex94a according to the present invention.
An average inclination xcex94a measured with a surface roughness meter is defined by a formula shown below which is described in sections 8-12 of chapter 8 xe2x80x9cdefinitions terms and parameters of surface roughnessxe2x80x9d of an instruction manual for Surface Roughness Meter SE-3300 manufactured by Kosaka Laboratory Co., Ltd. (manufactured in March, 1993).                               Δ          ⁢                      xe2x80x83                    ⁢          a                =                              (                          1              /              L                        )                    ⁢                                    ∫              0              L                        ⁢                                          "LeftBracketingBar"                                                      ⅆ                                          /                                              xe2x80x83                                            ⁢                                              ⅆ                        x                                                                              ·                                      f                    ⁡                                          (                      x                      )                                                                      "RightBracketingBar"                            ⁢                              ⅆ                x                                                                         less than                   Equation          ⁢                      xe2x80x83                    ⁢          1                 greater than             
On the other hand, the average inclination xcex94a within the range of 10 xcexcmxc3x9710 xcexcm according to the present invention indicates a value which is calculated from a three dimensional form with the atomic force microscope (AFM) (Q-SCOPE) 250 manufactured by Quesant Co. (version 3.181)).
Two dimensional average inclinations xcex94a of optional sectional curves which were calculated by the inventor at al. from three dimensional forms measured with the above described atomic force microscope were generally coincident with average inclinations xcex94a within the range of 10 xcexcmxc3x9710 xcexcm which were calculated from three dimensional forms. From viewpoints of a stability of measured values and a correlation with the toner adhesion preventing effect, however, the average inclinations xcex94a calculated from the three dimensional forms are more preferable.
However, the present invention is not limited by the average inclination xcex94a within the range of 10 xcexcmxc3x9710 xcexcm which are calculated from the three dimensional forms.
Atomic force microscopy which provides a horizontal resolution (resolution in a direction in parallel with a sample surface) higher than 0.5 nm and vertical resolution (resolution in a direction perpendicular to the sample surface) of 0.01 to 0.02 nm, permits measuring a three dimensional form of a sample and is largely different in the high resolution from a surface roughness meter which has conventionally been used widely.
At the resolution which is so high, it is possible to measure roughness not on the order which is governed by roughness of a substrate of a photosensitive member but roughness resulting from natures of deposited films themselves such as a photoconductive layer and a surface layer.
The roughness of the substrate of the photosensitive member is dependent on xe2x80x9ctypesxe2x80x9d such as xe2x80x9ctooth formxe2x80x9d and xe2x80x9ctreating memberxe2x80x9d of the above described lathe, ball mill and dimple treating work, whereas the roughness of the deposited films themselves has no xe2x80x9ctypexe2x80x9d, but form factors which cannot be expressed by Rz (average roughness along centerline) and Ra (average roughness at ten points) specified by JIS and the inventor et al. considered that the form factors would give a first step to the above described toner adhesion prevention. Specifically, the inventor et al. formed amorphous silicon photosensitive member (total layers including inhibition layers, photoconductive layers, surface layers and interfaces among these layers) in various conditions on electrically conductive substrates having surface roughness Ra not lower than 9 nm within an identical visual field range of (10 xcexcmxc3x9710 xcexcm), observed fine shapes on surfaces with an atomic force microscope, and calculated and compared average inclinations xcex94a for examination.
Since significant differences could not observed in similar measurements with a surface roughness meter which has conventionally been used widely, for example, a surface roughness meter (SE-3400) manufactured by Kosaka Laboratory Co., Ltd., it is considered that an index used for the present invention is a new index which represents characteristics of materials of amorphous silicon photosensitive members.
In addition, the inventor et al. measured several samples with several scan sizes with the atomic force microscope. The scan size is a length of a side of a scanned rectangle. A scan size of 10 xcexcm therefore means a scanned area of 10 xcexcmxc3x9710 xcexcm, that is, 100 xcexcm2. FIG. 2 shows some results obtained by checking a relation between the scan size and the average inclination xcex94a, the abscissa of the graph representing the scan size.
Measured values are stabilized but fine shapes can hardly be reflected under influences due to special shapes such as undulations, protrusions and the like as well as worked shapes of sample substrates when a scan size is large, that is, when the measuring range is large, and a selection variation of measuring locations is large when a scan size is small, whereby the present invention indicates the average inclinations in the visual field of 10 xcexcmxc3x9710 xcexcm which is excellent from an overall viewpoint of detecting performance and a stability of measurements.
Therefore, an inventive concept of the present invention is not always limited by the visual field of 10 xcexcmxc3x9710 xcexcm.
In order to obtain xcex94a which is preferable for the present invention, it is effective to adjust parameters of manufacturing conditions such as a high-frequency electric power and a frequency of the electric power, a pulse variation of the high-frequency electric power, a gas flow rate, a pressure, a substrate temperature and film thicknesses at stages of forming functional layers such as an inhibition layer, a photoconductive layer and a surface protective layer on a substrate by a high-frequency plasma CVD (PCVD) method. As a requirement for forming a deposited film surface having a large xcex94a, there can be the case where (1) a precursor of film formation which reaches a grown surface of a deposited film is not diffused sufficiently on the surface, or the precursor reaches in a large amount and a time is insufficient for the precursor to be dispersed on the surface or (2) a film is deposited in a condition where a gas phase polymerization reaction easily occurs and while taking a polymer produced in a gas phase. Specifically, conceivable as the requirement for forming the deposited film surface having the large xcex94a is to increase the high-frequency electric power, increase the gas flow rate, enhance the pressure, lower the substrate temperature, thicken the film thickness or the like. In such manufacturing conditions, however a quality of a deposited film may be degraded and a sufficient electrophotographic characteristic is not obtained when an a-Si photosensitive member is manufactured, thereby lowering an yield. In order to form an a-Si photosensitive member having a large xcex94a, it is therefore indispensable to adjust the parameters of the manufacturing conditions carefully so that a quality of a deposited film is not degraded as far as possible.
Though it is preferable that the manufacturing conditions for obtaining the deposited film having the large xcex94a are adopted for the photoconductive layer which occupies a most portion of a photosensitive member from a viewpoint of an effect of the manufacturing conditions, the conditions for controlling the xcex94a may be adopted only for the inhibition layer and the surface protective layer which produce little influence on the electrophotographic characteristic.
Furthermore, the average inclination xcex94a within a range preferable for the present can be obtained also by performing a post-treatment such as abrasion as occasion demands after depositing a film. Needless to say, the abrasion is performed while being appropriately adjusted dependently on a characteristic of the deposited film as well as depositing condition of the film. Using a tape to which fine particles of SiC are adhered (SiC abrading tape), for example, the abrasion can be performed by rubbing a surface of the surface of the photosensitive member on which film is deposited.
Specifically, a method described below can be used for obtaining surface roughness within the range of xcex94a=0.12 to 1.0 preferable for the present invention.
For example, there is a method which obtains a desired xcex94a by abrading the surface of the photosensitive member by dry or wet abrasion using as an abradant fine powder of silica, chromium oxide, titanium oxide, iron oxide, zirconium oxide, diamond, nitrogen carbide, silicon carbide, silicon nitride, serium oxide or the like. Furthermore, there is available a method which obtains a desired xcex94a by buffing, magnetic abrasion, magnetic fluid FFF, FFF utilizing electroemphoresis, FFF utilizing plasma (FFF: Field assisted Fine Finishing), EEH (Elastic Emission Haching) or abrasion with a wrapping film. This method permits reducing xcex94a when it is larger than a desired value.
FIG. 11 is a diagram descriptive of an apparatus for abrading a surface of a electrophotographic photosensitive member.
Reference numeral 1 denotes an electrophotographic photosensitive drum on a surface of which a surface layer to be treated is disposed. Reference numeral 2 denotes an abrading tape having an abrading surface over which crystalline SiC is coated (trade name: WRAPPING TAPE LT-C2000, manufacturer: Fuji Film). Reference numeral 3 denotes a cylindrical supporting body which brings the abrading tape 2 into contact with the surface of the photosensitive drum 1.
In addition to the tape having the abrading surface over which the crystalline SiC is coated, usable as abrading tapes preferable for the present invention is a tape over which powder of iron oxide, alumina, diamond or the like is coated. Reference numeral 4 denotes a cradle for the cylindrical supporting body 3 which is disposed in parallel with a rotating shaft of the photosensitive drum 1 and is loaded with a weight 5. Reference numeral 6 denotes a feeding motor which feeds out the abrading tape 2, thereby being sent at the definite speed while being pulled by a weight 7. Since the abrading tape is sent in a forward direction of a rotation of the photosensitive member at this stage, the surface layer is abraded without accumulating abraded power of SiC or a foreign matter in a gap between the abrading tape 2 and the photosensitive drum 1, and a desired xcex94a can be obtained. This method permits reducing a xcex94a when it has a value larger than desired. FIG. 12 is a sectional view of the abrading apparatus taken along a 12xe2x80x9412 line in FIG. 11. The photosensitive drum 1 is movable in a direction of a rotating shaft (X direction). Alternately, the abrading tape 2 or the cylindrical supporting body 3 may be moved. Accordingly, the abrading apparatus is capable of performing two-dimensional abrasion control and permits easily obtaining a desired xcex94a.